First commercialized in the early 1990's, lithium-ion batteries are now ubiquitous. They power everything from cellphones to laptop computers to electric cars. The rapid growth of this new type of battery was sparked by several advantages including higher energy density, relatively high cell voltage, and longer charge retention or shelf life.
There are many variations of lithium ion batteries, but they all rely on the same basic chemistry. A positive electrode is made of an intercalation compound such as lithium cobalt oxide, and a negative electrode typically is lithium graphite. The electrolyte is a solution of a lithium salt such as lithium phosphorus fluoride dissolved in an aprotic organic solvent like propylene carbonate. During the operation of the cell as it is repeatedly charged and discharged, lithium ions shuttle back and forth between the positive and negative electrodes.
In spite of the successes with lithium-ion batteries, these cells have a number of drawbacks. For one, they have a low rate of discharge or power capability. Second, they have limited cycle life. And finally, they have exhibited safety problems due to the flammability of their components. Not to be overlooked, the relative high cost of lithium-ion batteries has slowed their acceptance into new applications.
For these and other reasons there is a compelling need to find an improved secondary battery. The ideal battery would retain the best features of the lithium-ion battery but avoid or minimize its disadvantages. Therefore, it is a goal of the present invention to provide such a step forward in battery technology. These and other objects, features and advantages of the present invention will be recognized from the following description and the accompanying FIGURE.